Biopesticides are increasingly finding use in agricultural and horticultural settings for pest control. The potential benefit of biopesticides, especially relative to chemical pesticides, continues to spur the search for new biocontrol agents. For example, biopesticides create less pollution and environmental hazards than chemical pesticides. Further biopesticides appear to cause less problem with the development of drug resistance.
One significant agricultural pest amenable to control using biopesticides is the nematode. Nematode damage to crops is estimated to be more than $3 billion per year yet only about $180 million per year is spent in combating nematode diseases. Since chemical pesticide control of nematodes is relatively expensive, it is thus only used on high value crops. Effective biocontrol agents for nematodes, which are generally much cheaper to produce, thus promise to improve economic yield for a wider variety of crops.
Bacillus thuringiensis (Bt) strains are common insecticidal biocontrol agents, producing a polypeptide toxin which is deposited in crystalline inclusion bodies in the organism. However, the level of toxicity of both the Bt strains and the isolated toxin varies considerably, with some Bt strains failing to show insecticidal or other toxic activity (U.S. Pat. No. 4,948,734).
The effects of Bt as a nematocidal biocontrol agent have been investigated for free living nematodes, animal-parasitic nematodes, insect-parasitic nematodes and plant-parasitic nematodes. The strains Bt israelensis, Bt kurstaki and Bt morrisoni show considerable variability with respect to lethality for animal-parasitic and free living nematodes [Bottjer et al. (1985) Exp. Parasitol. 60: 239-244; Meadows et al. (1990) Invert. Reprod. Develop. 17: 73-76]. Similarly, two commercially available strains of Bt (SAN 415 and Dipel) show different toxicity effects as biocontrol agents for the plant-parasitic nematodes Meloidogyne javanica and Tylenchulus semipenetrans [Osman et al. (1988) Anz. Schadlingskde., Pflanzenschutz, Umweltschutz 61: 35-37].
While, Bt strains can be effective nematocidal agents, with the demonstrated variability in the Bt strains, there exists a need for additional Bt biopesticides to control the many nematodes that infect plants, especially economically important crop plants.